Not Applicable
Not Applicable
Not Applicable
1. Description of Related Art
A conventional grinding tool includes a grinding cup fastened to a rotary spindle, there being a vibration damping device between the spindle and grinding cup.
When grinding cemented carbide buttons of a drill bit, a grinding cup is normally used. The wear part of such grinding cup usually has an abrasive grinding surface that often comprises diamond particles. Grinding of cemented carbide buttons generates both heat and abrasive cuttings to such an extent that it is necessary to cool the grinding cup and the button bit as well as to flush away the cuttings. A prior art means for cooling involves supplying cooling medium, normally water, through the grinding machine and axially through the grinding cup to discharge the cooling medium in the region where the wear part of the grinding cup engages the free end of the button, as is shown in U.S. Pat. No. 5,964,649.
Through for example U.S. Pat. No. 5,688,163, there is previously known a tool for grinding buttons of a rock drill bit. The tool is secured to a grinding head, wherein the rotatably journalled spindle carries a grinding cup. The grinding cup is vibration-damped by means of a bushing of rubber for minimizing the risk for white fingers. Furthermore, the prior art grinding tool comprises means for quickly mounting and dismounting the grinding cup on and from the grinding spindle. Said means comprises an external, movable sleeve, a spring, a ball in a radial hole in the spindle, an O-ring and driving surfaces. This complicates the design of the grinding tool and requires two hands for demounting of the grinding cup.
Through for example U.S. Pat. No. 5,727,994 there is previously known a tool for grinding buttons of a rock drill bit. Also this grinding tool comprises means for quickly mounting and dismounting the grinding cup on and from the grinding spindle. Said means comprises an O-ring that co-operates with a cylindrical surface and polygonal co-operative surfaces for driving. In case a flush medium is supplied to the grinding cup without the grinding cup abutting against a button being ground, the pressure can influence the grinding cup from the inside which over-powers the frictional force between the O-ring and the grinding cup. Thus the grinding cup will become dislodged from the grinding spindle. In addition some skill is needed for aligning the driving surfaces when mounting the grinding cup.
2. Field of the Invention
The present invention relates to a grinding tool for grinding buttons of a rock drill bit, a grinding cup, a grinding spindle and a method for mounting the grinding cup on a grinding spindle.
One object of the present invention is to provide a grinding tool for grinding drill bit buttons, which realizes the advantages of the prior art,
Another object of the present invention is to provide a grinding tool that can be mounted or dismantled quickly.
Another object of the present invention is to provide a grinding tool that comprises a minimum of parts.
Another object of the present invention is to provide a grinding tool, which can be mounted or dismounted by means of one hand only.
Another object of the present invention is to provide a grinding tool which is developed such that the grinding cup is retained harder as more torque is applied.
The objects of the present invention are realized by a grinding tool for grinding buttons of a rock drill bit, a grinding cup, a spindle and a method of mounting the grinding cup on a spindle. The grinding tool comprises a spindle having a longitudinal axis of rotation, and a grinding cup mounted on the spindle by a tongue-and-socket connection which includes a cylindrical surface disposed on the grinding cup, the surface being symmetrical with respect to the axis. A vibration damper is disposed between the grinding cup and the spindle. A fastener secures the grinding cup to the spindle. The fastener is attached to the spindle against axial displacement relative thereto. The fastener is arranged to engage the cylindrical surface of the grinding cup to rotate the grinding cup when the spindle is rotated in a working direction. The fastener is arranged to tighten a grip on the grinding cup when the spindle is rotated in the working direction during a grinding operation, and to permit rotation of the grinding head relative to the spindle in the working direction to loosen a grinding head for insertion and removal thereof.
In another aspect of the invention the grinding cup has a body defining an axis of rotation and includes a forward wear part and a rear shank. A flush channel extends through the shank. The shank includes a cylindrical surface arranged symmetrically relative to the axis and defining a sole means of receiving a rotary drive torque during a grinding operation.
In another aspect of the invention an apparatus is provided for holding an insert-grinding cup. The apparatus comprises a grinding spindle which defines an axis of rotation and includes a cylindrical surface at one end thereof adapted to receive a grinding cup. The apparatus also includes a fastener for securing a grinding cup. The fastener is disposed against the cylindrical surface and is attached against axial movement relative to the spindle. The fastener is arranged to permit movement of a grinding cup relative to the spindle in a direction corresponding to a working direction of the spindle.
The invention also pertains a method for mounting a grinding cup on a grinding spindle for grinding buttons of a rock drill bit. The grinding spindle includes a first cylindrical surface. The grinding cup includes a forward wear part and a rear shank having a second cylindrical surface connectable to the first cylindrical surface. A coil spring fastener is provided for interconnecting the first and second cylindrical surfaces. The method comprises the steps of:
A. attaching the coil spring fastener to the grinding spindle such that the fastener is immovable relative thereto in the axial direction;
B. positioning a vibration-damping element between the spindle and the grinding cup; and
C. moving the grinding cup axially into engagement with the spindle while rotating the grinding cup relative to the spindle in a direction corresponding to a working direction of the spindle to elastically loosen the coil spring fastener and permit the grinding cup to be axially inserted onto the spindle,
wherein step A can be performed prior to, or after, step B.